Turbulence characteristics and dispersion in a forest—tests of Thomsonʹs random-flight model

A dispersion experiment, where the tracer SF6 was released from line sources, was carried out within a young pine forest. Line sources made of silicone tubes were installed at different heights and distances from a tower. Vertical concentration profiles were measured on the tower and the samples were analysed with a gas chromatograph. The measured concentration profiles were compared to those calculated using Thomsonʹs random-flight model. To provide input information to the model on turbulence, the turbulence characteristics were measured at four different heights with sonic anemometers. Data are presented for standard deviations of the velocity components, the momentum flux, the Lagrangian time scale and the mean horizontal wind velocity, depending on height and thermal stability. The derived turbulence characteristics resemble previous results in the literature; but are still stand specific. Satisfactory agreement was obtained between the measured and simulated SF6 concentration profiles. However, the model clearly underestimates the concentrations in the upper part of the stand. The results should add more confidence to the continued use of Thomsonʹs model and are useful for planning better dispersion experiments.